March 2011

Had jury duty yesterday, so I couldn’t make a map! I’m a bit lucky that I held out as models are finally figuring this storm out and cutting down precipitation totals significantly in PA and NJ. This is mostly due to later cyclogenesis and less moisture available since it was cut off by convection in the Southeast. The green area is where I think there will be SOME snow accumulation at the end of the event, but it won’t be enough to break into the 1″ contour.

Verification for the past storms and this one coming this weekend (hopefully). There will also be a discussion on a significant severe weather event that’s progged to rake the ArkLaTex region into the Southeast on Monday before progressing to the East Coast on Tuesday.

This will probably be my only forecast for the event, but if things unfold drastically different in the morning I will make some adjustments. Models keep showing accumulating snow through northern VA into MD, but the thicknesses and surface temperatures just aren’t there to realize the snowfall potential. It’ll be a cold, cold rain for most.

A mess of storms in the East – Forecasters and weather models alike are trying to wrap their collective heads around a series of systems which could bring a variety of precipitation patterns to the eastern U.S. by the end of the week.

The cold pattern tries to end – The cold will ease off going into early next week as above normal temperatures take its place across the South and the Southeast.

Very warm in the west – Much above normal temperatures will sit over the western U.S. during the second half of the week before belows return over the weekend.

—–Discussion:

The NAM appears to be in another world when compared to the GFS and ECMWF models going through mid-week. The models offer three rather different solutions in how to handle a series of three low pressure systems that will impact the eastern U.S. in quick succession Tuesday through Saturday. Right now it looks to be mostly rain, with the potential for a small area to see relatively big snowfall accumulation on the order of 6-12 inches. Whether or not any of that will verify will have to be determined in the coming days.

After this string of systems moves out of the East, a massive surge of warm air will form over the West during the second half of the work week. This ridge of warm air will translate into the East at the beginning of next week, which will hopefully start a prolonged period of near normal to above normal temperatures from the Southern Plains through the Southeast, southern Midwest and southern Mid-Atlantic. The northern U.S. may miss out on the prolonged warmth and head back into normal to below normal conditions after the upper-level ridge subsides a bit.

More on the regional impacts of these chilly storms in the East as the pattern becomes clearer.

After bombing last night’s snowfall forecast (verification coming later… it was way too dry and the rates were too low for most to see accumulation), it’s time to pick up the pieces and look at what we’ve got coming in the week ahead.

Skies will cloud up in the southern half of the region tonight as rain and maybe some mixed precipitation move through south of D.C. tomorrow. Precipitation totals should stay on the lighter side. Tuesday will be mostly sunny but still cool as high pressure quickly passes over the region, with another system bringing in light to moderate rain late Tuesday night into Wednesday. The northernmost parts of the region could see some wintry precipitation mix in.

Guidance begins struggling with the weather pattern as we head into Thursday, but the general idea is that clouds will linger over the region on Thursday as a coastal system develops on Friday. Right now it’s looking like it should stay as rain on Friday, with some frozen precipitation in the mountains. I would be screaming “OMG snowstorm!” if this was January, but the surface temperatures will probably not be there for this one. However, if this storm can pull enough cold air down from the north, we could be talking about a different story. This could be Mother Nature’s April Fools’ joke as winter’s last hurrah.

Temperatures will warm up as we head into Sunday. It’s unclear whether or not the warmer pattern will stick around going into next week, but the trends are currently to the cooler side past this short period of warmth.

Decided to shrink down the snow totals a bit for the 1-2″ range on the NE edge and for the 2-4″ range for the eastern and southern areas. The 4-8″ actually expanded a bit, but got shifted further south. It will be a battle of boundary layer temperatures and thicknesses tonight.

A suppressed storm system will move through the region Saturday into Sunday as a vort. max travels east-to-west over northern VA into MD. The SFC low is progged to move across the Carolinas, which will be favorable in getting a layer of below-zero temperatures at the SFC. However, it should be noted that the winds in the mid to upper levels will be out of the WSW across the southern parts of the region, which could allow for a nose of above freezing temperatures to move into southern WV and VA. This will cause mixing issues with sleet and freezing rain that will hurt the overall snowfall totals across the southernmost parts of the region. The wintry mix will extend into northern NC before changing over to all rain in central NC.

I am siding with the GFS snowfall contouring for now since it seems like it has a better handle on the mid-level temperatures and the warm nose that will move through the southern parts of the region. I also did account for a slight northerly trend in the eastern parts of the region, which is consistent with trends that yesterday’s storm experienced further north into NY and southern Canada, where accumulations occurred a good distance further north than anticipated.

Risks: A northern trend could bring the 1″+ totals into southern PA, and a colder solution as depicted on the NAM could bring the rain/snow line a bit further south towards the VA/NC border.

A rather unusual severe weather setup as a low pressure system rides along a frontal boundary that is NW-SE oriented from central OH into central MD. Warm-sector instability on the order of 500-1000+ J/kg SBCAPE will develop over WV and western VA during the afternoon, which will help initiate a few areas of showers and storms. A convergence area over the Appalachians will help trigger storms early, with better instability upstream ahead of the southward-moving cold front that will move through OH and WV during the late afternoon and early evening. Things will look a little messy on radar at first, but eventually some strong/severe cells will form in the westernmost parts of the region. The main threat from these storms will be hail and wind damage, with an isolated threat for a few tornadoes. Speed shear is good with this system, but winds will be largely unidirectional, which will hinder tornadic development. Upper-levels are somewhat favorable as left-exit region divergence and some support from the 500mb vort. provide good synoptic lift.

As these storms push east into the Apps. and coastal plain, they will likely lose some intensity as the surface instability wanes. However, elevated instability should be sufficient to maintain thunderstorms with hail (maybe severe) and gusty winds (likely not severe) as the storms reach the DC/BWI region in the early evening. Depending on the amount of the elevated CAPE, storms could maintain themselves rather well and provide the area with a good lightning show.

Chase-wise, I’m considering taking I-68 to Morgantown, WV and then waiting to see where storms initiate. Should storms end up more favorable to the south, it will be a quick drive on I-79 towards Charleston, WV to get into better position.

—–THIS WEEKEND:

It appears as though the cold air is a lock for Friday and Saturday. A storm system passing by to our south on Saturday is expected to bring some cold rain and possibly snow into the region (…so much for that Southeast ridge). Should the colder temperatures and precipitation verify, a swath of 1-3″ or more of snow is possible in the northern half of the region. Timing the precipitation with the colder temperatures will be key in getting widespread snowfall to occur, so this system will be revisited later this week and could include a snowfall forecast map.

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I will forgo this week’s What to Watch Fore(cast) as 1) I am already behind and 2) there’s plenty to track regionally this week.